A radial turbine is a turbine in which the flow of the working fluid is radial to the shaft. The flow is smoothly orientated at 90 degrees by a compressor towards the plane of working blades as well as towards the axis of the turbine shaft. As a result, in radial turbines there is less mechanical complexity and thermal stress as compared to axial turbines, which enables a radial turbine to be simpler, more robust and more cost effective especially for low power applications.
A PCT application WO2009109020 discloses a radial turbine, comprising discs with cavities, mounted alongside discs with smooth surfaces, to form channels for the working fluid and receive the kinetic impact on the surface substantially perpendicular to the direction of the working fluid, which results in the rotation of the whole rotor.
A U.S. Pat. No. 6,973,792 discloses an engine comprising multiple discs mounted coaxially next to each other, in one embodiment the discs being covered with a catalyst layer. Each catalyst layer is etched such that at least one channel is formed between the discs. This allows, among others, for production of hydrogen, as well as to use the energy of the incoming medium for rotating the output shaft.
There is also known a bladeless turbine, invented by Nicola Tesla, which is a radial turbine using a boundary layer effect, occurring between smooth, uninterrupted surfaces of thin discs arranged closely next to each other and mounted coaxially on said shaft, provided with the working medium tangentially to their circumference. The turbine has several advantages, one of them being an ability to self-start while using only the energy of incoming medium. The other advantages are a relatively high expansion ratio and a high efficiency in applications when working under small loads.
A U.S. Pat. No. 1,061,206 discloses a radial bladeless turbine of the above-discussed type, comprising a number of discs aligned close to each other and provided, through a nozzle, with the working medium, e.g. steam, tangentially to the circumference of the rotor discs and perpendicular to its shaft. The discs have openings located in their center parts, providing the exit for the working medium. This bladeless construction results in a comparatively low torque. Not only is the maximum achievable torque relatively low, but it requires high rotational speed. On top of that the original Tesla turbine requires discs produced and assembled with high precision, so as to prevent the irregularities in the space created between them, which irregularities may be causing turbulences in the flow of the working medium, and what eventually may decrease its overall efficiency.
A US application US2011/0164958 discloses a radial turbine utilizing several forces resulting from a pressurized working medium provided through a nozzle substantially tangentially to the rotors circumference. One of these forces is a frictional (viscous) force. The turbine comprises a plurality of discs, mounted in a short distance to each other, with spacer discs placed between them. The shape of the discs results in formation of spiral channels after assembly. The turbine is configured to be operated with fluids of extremely low kinematic viscosity.
A PCT application WO2009/088955 discloses a radial turbine utilizing a frictional (viscous) force. It comprises a plurality of discs, mounted close to each other. One of the features discussed in WO2009/088955 concerns the distance between the discs, dependent on the thickness of the boundary layer of the fluid used to propel the turbine. This indicates that to improve the turbine efficiency, the discs shall be spaced close to each other.